The present invention relates to an optical switching device. More particularly, the present invention relates to an optical switching device that comprises a switching element integrated with an optical detector and the method for making such device.
An optical switch switches light energy from one optical path to another. U.S. Pat. No. 4,728,167 to Soref et al. that issued on Mar. 1, 1988 is directed to an electrically controlled integrated optical switch. The body of the switch is made of crystalline silicon and has an X-shaped channel waveguide structure forming an intersection crossover region. The index of refraction of the intersection crossover region is altered by changing the current or voltage supplied to the electrodes located at the intersection crossover region. This changes the amount of optical cross coupling of light between the intersecting waveguides. Crystalline semiconductor waveguide optical switches having at least one optical waveguide formed within a core layer made of a crystalline semiconductor are known. The waveguide absorbs controlling light when an electric field is applied, and a pair of electrodes are formed for applying a voltage to a waveguide part to manipulate the index of refraction.
The limitations of known optical switches, however, do not adequately satisfy the demands of optical telecommunications. In telecommunications applications, switching takes place in the electrical domain rather than in the optical domain, because sufficiently fast and cost-effective optical switches are unavailable. A smart, fast, integrated, cost effective optical switch is needed to meet the demands of high performance optical networks and access networks, including a switch enabling packet switching in the optical domain.
An optical switch according to the principles of the invention is an integrated optical switch including a switching element and an optical detector in communication with the switching element. The optical detector processes header information from an optical packet to operate the switch and route the payload. A single switch element can be made from two planar waveguides. By adjusting a voltage applied to one waveguide relative to the other, a phase shift between the waveguide modes can be controlled by refractive index change induced by charge injection. Multiple switch elements can be combined to form a switch fabric, such as an Nxc3x97N fabric.
The optical detector can be a PIN diode built on top of the input waveguide to the switch and comprising semiconductor material having a higher index of refraction than the waveguide material. Light leaking into the diode is converted to an electrical signal which can be processed to extract the header information and control the switch. In an exemplary embodiment, the input waveguide comprises aSi:H and the PIN diode comprises a-Ge. The waveguide is built on a c-Si substrate. Integrated logic circuitry responsive to the electrical signal provided by the PIN diode can be fabricated on the c-Si substrate, and operates to interpret the address information from the optical header. A voltage applied across the waveguides changes the appropriate index of refraction to cause switching the light energy from one waveguide to the other via induced charge injection. A second PIN diode in the waveguide creates the induced charge injection. The resulting detector and switch element provides sufficiently fast switching to route packets in the optical domain.